Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels.
Particulate matter sensors may correlate a measured change in electrical conductivity (or resistivity) between a pair of electrodes placed on a substrate surface of the sensor with the amount of particulate matter deposited between the electrodes. Particulate matter sensors may encounter problems with non-uniform deposition of soot on the sensor due to a bias in flow distribution across the surface of the sensor. Further, particulate matter sensors may be prone to contamination from an impingement of water droplets and/or larger particulates present in the exhaust gases. This contamination may lead to errors in sensor output.
Other attempts to address particulate matter sensor deposition include shielding the sensor with a tube. One example approach is shown by Nelson et al. in U.S. Pat. No. 8,225,548. Therein, a PM sensor includes a flow redirector and a barrier positioned around a PM sensor element to filter out the larger particulates from impinging the PM sensor element. The barrier thus serves to block larger particulates in the exhaust flow from impinging on the PM sensor element, thereby reducing PM sensor sensitivity fluctuations due to large particulates depositing on the PM sensor element.
However, the inventors herein have recognized potential issues with systems such as Nelson. As one example, planar substrate surfaces may be susceptible to uneven particulate matter (PM) deposition due to the surface receiving exhaust gas from a small portion of the sensor device. Furthermore, an opening of the sensor tube faces an upstream direction relative to a direction of exhaust gas flow. This allows large particulates to readily flow into the sensor tube, which may inadvertently accumulate onto the sensor despite a design of the sensor tube.
The inventors herein have recognized the above issues and identified an approach to at least partly address both the general issues as well as particular issues with Nelson. In one example, the issues described above may be addressed by a system comprising a plurality of hollow discs increasing in diameter along a vertical axis, a first electrode installed on surfaces of each alternating disc of the plurality of discs, a second electrode installed on surfaces of each remaining disc of the plurality of discs, and a tube with an inlet facing a downstream direction relative to engine exhaust flow. In this way, large particulates may not enter the tube due to their momentum while the discs capture particulate matter from a greater range of the tube compared to the prior art.
As one example, the discs may increase in size with respect to a direction of exhaust flow in the tube. An outer rim (edge) of larger discs may extend beyond an outer circumference of smaller discs, where the edges face a direction of exhaust flow in the tube. Particulate matter (PM) may deposit on the edges and bridge the first and second electrodes after exceeding a threshold PM load. Large particulates and/or water droplets may not flow through the tube due to the configuration of the tube opening and a greater momentum of large particulate/water droplets compared to smaller PM. Overall, functioning of the PM sensor may be improved and may be more reliable.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.